Method and apparatus for transmitting control information in wireless communication system

ABSTRACT

The present invention pertains to a wireless communication system, and more particularly, to a method of receiving a downlink (DL) control channel in a wireless communication system and an apparatus therefor, and the method comprises the following steps: receiving a radio resource control (RRC) message including resource block (RB) allocation information; receiving a subframe having a plurality of physical RBs; and monitoring a plurality of downlink control channel candidates in a physical RB set corresponding to the RB allocation information from the plurality of physical RBs to detect a downlink control channel allocated to a communication device, wherein the plurality of downlink control channel candidates do not continuously exist in a virtual RB set corresponding to the physical RB set.

TECHNICAL FIELD

The present invention relates to a wireless communication system, andmore particularly, to a method and apparatus for transmitting controlinformation. The wireless communication system supports carrieraggregation (CA).

BACKGROUND ART

Wireless communication systems have been widely deployed to providevarious types of communication services including voice and dataservices. In general, a wireless communication system is a multipleaccess system that supports communication among multiple users bysharing available system resources (e.g. bandwidth, transmit power,etc.) among the multiple users. The multiple access system may adopt amultiple access scheme such as code division multiple access (CDMA),frequency division multiple access (FDMA), time division multiple access(TDMA), orthogonal frequency division multiple access (OFDMA), or singlecarrier frequency division multiple access (SC-FDMA).

DISCLOSURE Technical Problem

An object of the present invention devised to solve the problem lies ina method for efficiently transmitting control information in a wirelesscommunication system and an apparatus for the same. Another object ofthe present invention is to provide a channel format, resourceallocation method and signal processing method for efficientlytransmitting control information and an apparatus for the same. Afurther object of the present invention is to provide a method forefficiently allocating resources for transmitting control informationand an apparatus for the same.

The technical problems solved by the present invention are not limitedto the above technical problems and those skilled in the art mayunderstand other technical problems from the following description.

Technical Solution

The object of the present invention can be achieved by providing amethod for receiving a downlink control channel by a communicationdevice in a wireless communication system, the method including:receiving a radio resource control (RRC) message including resourceblock (RB) allocation information; receiving a subframe having aplurality of physical RBs; and monitoring a plurality of downlinkcontrol channel candidates in a physical RB set corresponding to the RBallocation information from among the plurality of physical RBs todetect a downlink control channel allocated to the communication device,wherein the plurality of downlink control channel candidates arenon-consecutively present in a virtual RB set corresponding to thephysical RB set.

In another aspect of the present invention, provided herein is acommunication device for use in a wireless communication system,including: a radio frequency (RF) unit; and a processor, wherein theprocessor is configured to receive an RRC message including RBallocation information, to receive a subframe having a plurality ofphysical RBs and to monitor a plurality of downlink control channelcandidates in a physical RB set corresponding to the RB allocationinformation from among the plurality of physical RBs to detect adownlink control channel allocated to the communication device, whereinthe plurality of downlink control channel candidates arenon-consecutively present in a virtual RB set corresponding to thephysical RB set.

The plurality of downlink control channel candidates may benon-consecutively present in a plurality of sub-resources correspondingto the virtual RB set.

The plurality of downlink control channel candidates may beconsecutively present in a plurality of sub-resources corresponding tothe virtual RB set in the order of indices, wherein a plurality ofsub-resources included in one virtual RB are non-sequentially indexed.

An index difference between sub-resources included in one virtual RB maybe proportional to the number of RBs included in the virtual RB set.

The plurality of downlink control channel candidates may be presentafter a specific orthogonal frequency division multiplexing (OFDM)symbol in the subframe, and the specific OFDM symbol is not the firstOFDM symbol of the subframe.

Physical RBs other than the physical RB set from among the plurality ofphysical RBs may be resources for physical downlink shared channel(PDSCH) transmission.

The downlink control channel may include an enhanced physical downlinkcontrol channel (E-PDCCH).

Advantageous Effects

According to the present invention, it is possible to efficientlytransmit control information in a wireless communication system. Inaddition, it is possible to provide a channel format, resourceallocation method and signal processing method for efficientlytransmitting control information. Furthermore, it is possible toefficiently allocate resources for transmitting control information.

The effects of the present invention are not limited to theabove-described effects and other effects which are not described hereinwill become apparent to those skilled in the art from the followingdescription.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention, illustrate embodiments of the inventionand together with the description serve to explain the principle of theinvention. In the drawings:

FIG. 1 illustrates physical channels used in a 3GPP LTE system as awireless communication system and a signal transmission method using thesame;

FIG. 2 illustrates a radio frame structure;

FIG. 3 illustrates a resource grid of a downlink slot;

FIG. 4 illustrates a downlink subframe structure;

FIG. 5 illustrates a procedure through which a base station configures aPDCCH;

FIG. 6 illustrates a procedure through which a UE processes a PDCCH;

FIG. 7 illustrates an uplink subframe structure;

FIG. 8 illustrates a CA (carrier aggregation) communication system;

FIG. 9 illustrates cross-carrier scheduling;

FIG. 10 illustrates an example of allocating a PDCCH to a data region ofa subframe;

FIG. 11 illustrates a procedure for allocating resources for an E-PDCCHand receiving a PDSCH;

FIG. 12 is diagram for explaining problems when an E-PDCCH search spaceis configured;

FIGS. 13 to 25 illustrate examples of configuring an E-PDCCH searchspace according to embodiments of the present invention; and

FIG. 26 illustrates a base station (BS) and UE applicable to the presentinvention.

FIG. 27 illustrates a BS, a relay and a UE applicable to the presentinvention.

BEST MODE

Embodiments of the present invention are applicable to a variety ofwireless access technologies such as code division multiple access(CDMA), frequency division multiple access (FDMA), time divisionmultiple access (TDMA), orthogonal frequency division multiple access(OFDMA), and single carrier frequency division multiple access(SC-FDMA). CDMA can be implemented as a radio technology such asUniversal Terrestrial Radio Access (UTRA) or CDMA2000. TDMA can beimplemented as a radio technology such as Global System for Mobilecommunications (GSM)/General Packet Radio Service (GPRS)/Enhanced DataRates for GSM Evolution (EDGE). OFDMA can be implemented as a radiotechnology such as Institute of Electrical and Electronics Engineers(IEEE) 802.11 (Wireless Fidelity (Wi-Fi)), IEEE 802.16 (Worldwideinteroperability for Microwave Access (WiMAX)), IEEE 802.20, and EvolvedUTRA (E-UTRA). UTRA is a part of Universal Mobile TelecommunicationsSystem (UMTS). 3^(rd) Generation Partnership Project (3GPP) Long TermEvolution (LTE) is a part of Evolved UMTS (E-UMTS) using E-UTRA,employing OFDMA for downlink and SC-FDMA for uplink. LTE-Advanced(LTE-A) is evolved from 3GPP LTE. While the following description isgiven, centering on 3GPP LTE/LTE-A for clarity, this is purely exemplaryand thus should not be construed as limiting the present invention.

In a wireless communication system, a UE receives information from a BSon downlink (DL) and transmits information to the BS on uplink (UL).Information transmitted/received between the BS and UE includes data andvarious type of control information, and various physical channels arepresent according to type/purpose of information transmitted/receivedbetween the UE and BS.

FIG. 1 illustrates physical channels used in a 3GPP LTE system and asignal transmission method using the same.

When powered on or when a UE initially enters a cell, the UE performsinitial cell search involving synchronization with a BS in step S101.For initial cell search, the UE synchronizes with the BS and acquireinformation such as a cell Identifier (ID) by receiving a primarysynchronization channel (P-SCH) and a secondary synchronization channel(S-SCH) from the BS. Then the UE may receive broadcast information fromthe cell on a physical broadcast channel (PBCH). In the mean time, theUE may check a downlink channel status by receiving a downlink referencesignal (DL RS) during initial cell search.

After initial cell search, the UE may acquire more specific systeminformation by receiving a physical downlink control channel (PDCCH) andreceiving a physical downlink shared channel (PDSCH) based oninformation of the PDCCH in step S102.

The UE may perform a random access procedure to access the BS in stepsS103 to S106. For random access, the UE may transmit a preamble to theBS on a physical random access channel (PRACH) (S103) and receive aresponse message for preamble on a PDCCH and a PDSCH corresponding tothe PDCCH (S104). In the case of contention-based random access, the UEmay perform a contention resolution procedure by further transmittingthe PRACH (S105) and receiving a PDCCH and a PDSCH corresponding to thePDCCH (S106).

After the foregoing procedure, the UE may receive a PDCCH/PDSCH (S107)and transmit a physical uplink shared channel (PUSCH)/physical uplinkcontrol channel (PUCCH) (S108), as a general downlink/uplink signaltransmission procedure. Here, control information transmitted from theUE to the BS is called uplink control information (UCI). The UCI mayinclude a hybrid automatic repeat and request (HARQ)acknowledgement(ACK)/negative-ACK (HARQ ACK/NACK) signal, a schedulingrequest (SR), channel state information (CSI), etc. The CSI includes achannel quality indicator (CQI), a precoding matrix index (PMI), a rankindicator (RI), etc. While the UCI is transmitted through a PUCCH ingeneral, it may be transmitted through a PUSCH when control informationand traffic data need to be simultaneously transmitted. The UCI may beaperiodically transmitted through a PUSCH at the request/instruction ofa network.

FIG. 2 illustrates a radio frame structure. In a cellular OFDM wirelesspacket communication system, uplink/downlink data packet transmission isperformed on a subframe-by-subframe basis. A subframe is defined as apredetermined time interval including a plurality of OFDM symbols. 3GPPLTE supports a type-1 radio frame structure applicable to FDD (FrequencyDivision Duplex) and a type-2 radio frame structure applicable to TDD(Time Division Duplex).

FIG. 2(a) illustrates a type-1 radio frame structure. A downlinksubframe includes 10 subframes each of which includes 2 slots in thetime domain. A time for transmitting a subframe is defined as atransmission time interval (TTI). For example, each subframe has alength of 1 ms and each slot has a length of 0.5 ms. A slot includes aplurality of OFDM symbols in the time domain and includes a plurality ofresource blocks (RBs) in the frequency domain. Since downlink uses OFDMin 3GPP LTE, an OFDM symbol represents a symbol period. The OFDM symbolmay be called an SC-FDMA symbol or symbol period. An RB as a resourceallocation unit may include a plurality of consecutive subcarriers inone slot.

The number of OFDM symbols included in one slot may depend on cyclicprefix (CP) configuration. CPs include an extended CP and a normal CP.When an OFDM symbol is configured with the normal CP, for example, thenumber of OFDM symbols included in one slot may be 7. When an OFDMsymbol is configured with the extended CP, the length of one OFDM symbolincreases, and thus the number of OFDM symbols included in one slot issmaller than that in case of the normal CP. In case of the extended CP,the number of OFDM symbols allocated to one slot may be 6. When achannel state is unstable, such as a case in which a UE moves at a highspeed, the extended CP can be used to reduce inter-symbol interference.

When the normal CP is used, one subframe includes 14 OFDM symbols sinceone slot has 7 OFDM symbols. The first three OFDM symbols at most ineach subframe can be allocated to a PDCCH and the remaining OFDM symbolscan be allocated to a PDSCH.

FIG. 2(b) illustrates a type-2 radio frame structure. The type-2 radioframe includes 2 half frames. Each half frame includes 5 subframes. Asubframe may be one of a downlink subframe, an uplink subframe and aspecial subframe. The special subframe can be used as a downlinksubframe or an uplink subframe according to TDD configuration. Thespecial subframe includes a downlink pilot time slot (DwPTS), a guardperiod (GP), and an uplink pilot time slot (UpPTS). The DwPTS is usedfor initial cell search, synchronization or channel estimation in a UE.The UpPTS is used for channel estimation in a BS and UL transmissionsynchronization acquisition in a UE. The GP eliminates UL interferencecaused by multi-path delay of a DL signal between a UL and a DL.

The above-described radio frame structure is merely exemplary and thenumber of subframes included in the radio frame, the number of slotsincluded in a subframe, and the number of symbols included in a slot canbe vary.

FIG. 3 illustrates a resource grid of a downlink slot.

Referring to FIG. 3, a downlink slot includes a plurality of OFDMsymbols in the time domain. One downlink slot may include 7(6) OFDMsymbols, and one resource block (RB) may include 12 subcarriers in thefrequency domain. Each element on the resource grid is referred to as aresource element (RE). One RB includes 12×7(6) REs. The number N_(RB) ofRBs included in the downlink slot depends on a downlink transmitbandwidth. The structure of an uplink slot may be same as that of thedownlink slot.

FIG. 4 illustrates a downlink subframe structure.

Referring to FIG. 4, a maximum of 3 OFDM symbols located in a frontportion of a first slot within a subframe correspond to a control regionto which a control channel is allocated. The remaining OFDM symbolscorrespond to a data region to which a physical downlink shared chancel(PDSCH) is allocated. Examples of downlink control channels used in LTEinclude a physical control format indicator channel (PCFICH), a physicaldownlink control channel (PDCCH), a physical hybrid ARQ indicatorchannel (PHICH), etc. The PCFICH is transmitted at a first OFDM symbolof a subframe and carries information regarding the number of OFDMsymbols used for transmission of control channels within the subframe.The PHICH is a response of uplink transmission and carries an HARQacknowledgment (ACK)/negative-acknowledgment (NACK) signal. Controlinformation transmitted through the PDCCH is referred to as downlinkcontrol information (DCI). The DCI includes uplink or downlinkscheduling information or an uplink transmit (Tx) power control commandfor a UE group.

A PDCCH may carry a transport format and a resource allocation of adownlink shared channel (DL-SCH), resource allocation information of anuplink shared channel (UL-SCH), paging information on a paging channel(PCH), system information on the DL-SCH, information on resourceallocation of an upper-layer control message such as a random accessresponse transmitted on the PDSCH, a set of Tx power control commands onindividual UEs within an arbitrary UE group, a Tx power control command,information on activation of a voice over IP (VoIP), etc. A plurality ofPDCCHs can be transmitted within a control region. The UE can monitorthe plurality of PDCCHs. The PDCCH is transmitted on an aggregation ofone or several consecutive control channel elements (CCEs). The CCE is alogical allocation unit used to provide the PDCCH with a coding ratebased on a state of a radio channel. The CCE corresponds to a pluralityof resource element groups (REGs). A format of the PDCCH and the numberof bits of the available PDCCH are determined by the number of CCEs. TheBS determines a PDCCH format according to DCI to be transmitted to theUE, and attaches a cyclic redundancy check (CRC) to control information.The CRC is masked with a unique identifier (referred to as a radionetwork temporary identifier (RNTI)) according to an owner or usage ofthe PDCCH. If the PDCCH is for a specific UE, a unique identifier (e.g.,cell-RNTI (C-RNTI)) of the UE may be masked to the CRC. Alternatively,if the PDCCH is for a paging message, a paging identifier (e.g.,paging-RNTI (P-RNTI)) may be masked to the CRC. If the PDCCH is forsystem information (more specifically, a system information block(SIB)), a system information RNTI (SI-RNTI) may be masked to the CRC.When the PDCCH is for a random access response, a random access-RNTI(RA-RNTI) may be masked to the CRC.

A PDCCH carries a message known as downlink control information (DCI)and DCI includes resource allocation information for a UE or UE groupand other control information. Typically, a plurality of PDCCHs can betransmitted in one subframe. Each PDCCH is transmitted using one or morecontrol channel elements (CCEs) each of which corresponds to 4 resourceelements of 9 sets. 4 resource elements correspond to a resource elementgroup (REG). 4 QPSK symbols are mapped to each REG. A resource elementallocated by a reference signal is not included in an REG, and thus thetotal number of REGs in predetermined OFDM symbols depends on presenceor absence of a cell-specific reference signal. The concept of REG (i.e.mapping on a group basis, each group including 4 resource elements) canbe used for other downlink control channels (PCFICH and PHICH). 4 PDCCHformats are supported as listed in Table 1.

TABLE 1 PDCCH Number of CCEs Number of Number of format (n) REGs PDCCHbits 0 1 9 72 1 2 18 144 2 4 36 288 3 8 72 576

CCEs are sequentially numbered. To simplify a decoding process,transmission of a PDCCH having a format including n CCEs can be startedusing as many CCEs as a multiple of n. The number of CCEs used totransmit a specific PDCCH is determined by a BS according to channelcondition. For example, if a PDCCH is for a UE having a high-qualitydownlink channel (e.g. a channel close to the BS), only one CCE can beused for PDCCH transmission. However, for a UE having a poor channel(e.g. a channel close to a cell edge), 8 CCEs can be used for PDCCHtransmission in order to obtain sufficient robustness. In addition, apower level of the PDCCH can be controlled according to channelcondition.

The approach adopted for LTE is to define for each UE a limited set ofCCE locations where a PDCCH may be placed. The set of CCE locations inwhich the UE may find PDCCHs thereof can be considered as a ‘searchspace (SS)’. In LTE, the search space is a different size for each PDCCHformat. Moreover, separate UE-specific and common search spaces aredefined. The UE-specific search space is configured for each UEindividually while all UEs are informed of the extent of the commonsearch space. The UE-specific search space and common search spaces mayoverlap for a given UE. With such small search spaces, it is quitepossible in a given subframe that the BS cannot find CCE resources tosend PDCCHs to all the UEs that it would like to, because havingassigned some CCE locations the remaining ones are not in the searchspace of a particular UE. To minimize the possibility of such blockingpersisting into the next subframe, a UE-specific hopping sequence isapplied to the starting positions of the UE-specific search spaces.

The sizes of the common and UE-specific search spaces are listed inTable 2.

TABLE 2 Number Number of Number of PDCCH of CCEs candidates incandidates in format (n) common search space dedicated search space 0 1— 6 1 2 — 6 2 4 4 2 3 8 2 2

In order to control the computational load arising from the total numberof blind decoding attempts, the UE is not required to search for all thedefined DCI formats simultaneously. Typically, in the UE-specific searchspace, the UE always searches for formats 0 and 1A, which are both thesame size and are distinguished by a flag in the message. In addition,the UE may be required to receive a further format (e.g. 1, 1B or 2depending on the PDSCH transmission mode configured by the BS. In thecommon search space, the UE searches for formats 1A and 1C. In additionthe UE may be configured to search for format 3 or 3A, which have thesame size as formats 0 and 1A, and may be distinguished by having CRCscrambled by a different (common) identifier, rather than a UE-specificidentifier. The transmission mode for configuring the multi-antennatechnique and the information content of DCI formats are listed below.

Transmission Mode

-   -   Transmission Mode 1: Transmission from a single BS antenna port    -   Transmission Mode 2: Transmit diversity    -   Transmission Mode 3: Open-loop spatial multiplexing    -   Transmission Mode 4: Closed-loop spatial multiplexing    -   Transmission Mode 5: Multi-user MIMO    -   Transmission Mode 6: Closed-loop rank-1 precoding    -   Transmission Mode 7: Transmission using UE-specific reference        signals

DCI Format

-   -   Format 0: Resource grants for the PUSCH transmissions (uplink)    -   Format 1: Resource assignments for single codeword PDSCH        transmissions (transmission modes 1, 2 and 7)    -   Format 1A: Compact signaling of resource assignments for single        codeword PDSCH (all modes)    -   Format 1B: Compact resource assignments for PDSCH using rank-1        closed loop precoding (mode 6)    -   Format 1C: Very compact resource assignments for PDSCH (e.g.        paging/broadcast system information)    -   Format ID: Compact resource assignments for PDSCH using        multi-user MIMO (mode 5)    -   Format 2: Resource assignments for PDSCH for closed-loop MIMO        operation (mode 4)    -   Format 2A: Resource assignments for PDSCH for open-loop MIMO        operation (mode 3)    -   Formats 3/3A: Power control commands for PUCCH and PUSCH with        2-bit/1-bit power adjustments

Considering the above, the UE is required to carry out a maximum of 44blind decoding operations in a subframe. This does not include checkingthe same message with different CRC values, which requires only a smalladditional computational complexity.

FIG. 5 is a flowchart illustrating a procedure through which the BSconfigures a PDCCH.

Referring to FIG. 5, the BS generates control information according toDCI format. The BS can select a DCI format from a plurality of DCIformats (DCI formats 1, 2, . . . , N) according to control informationto be transmitted to a UE. In step S410, a CRC (cyclic redundancy check)for error detection is attached to control information generated basedon each DCI format. The CRC is masked with an identifier (e.g. RNTI)according to an owner or usage of a PDCCH. In other words, the PDCCH isCRC-scrambled with the identifier (e.g. RNTI).

Table 3 shows examples of identifiers masking the PDCCH.

TABLE 3 Type Identifier Description UE- C-RNTI, temporary C-RNTI, Usedfor unique specific semi-persistent C-RNTI identification of UE CommonP-RNTI Used for paging messages SI-RNTI Used for system informationRA-RNTI Used for random access response

When C-RNTI, temporary C-RNTT or semi-persistent C-RNTT is used, thePDCCH carries control information for the corresponding UE. When otherRNTIs are used, the PDCCH carries common control information received byall UEs in a cell. In step S420, the CRC-attached control information ischannel-coded, generating coded data. In step S430, rate matching basedon a CCE aggregation level allocated to a PDCCH format is performed. Instep S440, the coded data is modulated to generate modulated symbols.Modulated symbols constituting a PDCCH may have one of CCE aggregationlevels of 1, 2, 4 and 8. In step S450, the modulated symbols are mappedto physical REs.

FIG. 6 is a flowchart illustrating a procedure through which the UEprocesses the PDCCH.

Referring to FIG. 6, the UE demaps the physical REs to CCEs in stepS510. The UE performs demodulation for each CCE aggregation level instep S520 since the UE does not know a CCE aggregation level at whichthe UE needs to receive the PDCCH. The UE performs rate dematching onthe demodulated data in step S530. The UE carries out rate dematchingfor each DIC format (or DCI payload size) since the UE does not know aDCI format (or DCI payload size) corresponding to information that needsto be received by the UE. The UE performs channel decoding on therate-dematched data according to coding rate and detects whether anerror is generated by checking the CRC in step S540. When no error isgenerated, the UE detects the PDCCH corresponding thereto. If the erroris generated, the UE continuously performs blind decoding for other CCEaggregation levels or other DCI formats (or DCI payload sizes). Upondetection of the PDCCH, the UE removes the CRC from the decoded data andacquires the control information in step S550.

A plurality of PDCCHs for a plurality of UEs can be transmitted in acontrol region of the same subframe. The BS does not provide informationabout the position of a PDCCH in the control region to a UEcorresponding to the PDCCH. Accordingly, the UE searches the subframefor the PDCCH thereof by monitoring a set of PDCCH candidates. Here,monitoring refers to a process through the UE attempts to decodereceived PDCCH candidates according to each DCI format. Monitoring isalso referred to as blind detection. The UE simultaneously performsidentification of the PDCCH transmitted thereto and decoding of controlinformation transmitted through the PDCCH using blind detection. Forexample, when the PDCCH is de-masked with C-RNTI, the UE detects thePDCCH thereof if no CRC error is generated.

To reduce blind detection overhead, the number of DCI formats is definedas smaller than the number of types of control information transmittedusing the PDCCH. DCI formats include different information fields.Information field type, the number of information fields and the numberof bits of each information field vary according to DCI format. Inaddition, the size of control information matched to a DCI formatdepends on the DCI format. A DCI format can be used to transmit two ormore types of control information.

Table 4 shows examples of control information transmitted using DCIformat 0. The bit size of each information field is exemplary and is notlimited to Table 4.

TABLE 4 Information field Bit(s) (1) Flag for discriminating between 1format0 and format 1A (2) Hopping flag 1 (3) Resource block allocationand ┌log₂(N_(RB) ^(UL)(N_(RB) ^(UL) + 1)/2)]┐ hopping resourceallocation (4) Modulation and coding scheme and 5 redundancy version (5)New data indicator 1 (6) TPC command for scheduled PUSCH 2 (7) Cyclicshift for DM RS 3 (8) UL index (TDD) 2 (9) CQI request 1

The flag field is an information flag for discriminating between format0 and format 1A. That is, DCI format 0 and DCI format 1A have the samepayload size and are discriminated from each other by flag fields. Thebit size of the resource block allocation and hopping resourceallocation field may vary according to hopping PUSCH or non-hoppingPUSCH. The resource block allocation and hopping resource allocationfield for the non-hopping PUSCH provides ┌log₂(N_(RB) ^(UL)(N_(RB)^(UL)+1)/2┐ bits for resource allocation of the first slot in an uplinksubframe. Here, N_(RB) ^(UL) denotes the number of RB s included in anuplink slot and depends on an uplink transmission bandwidth set in acell. Accordingly, the payload size of DCI format 0 can depend on anuplink bandwidth. DCI format 1A includes information field for PDSCHallocation. The payload size of the DCI format 1A can depend on adownlink bandwidth. DCI format 1A provides a reference information bitsize for DCI format 0. Accordingly, ‘0’ is added to DCI format 0 untilthe payload size of DCI format 0 becomes identical to the payload sizeof DCI format 1A when the number of information bits of DCI format 0 isless than the number of information bits of DCI format 1A. The added ‘0’is filled in a padding field of DCI format.

FIG. 7 illustrates an uplink subframe structure used in LTE.

Referring to FIG. 7, an uplink subframe includes a plurality of (e.g. 2)slots. A slot may include different numbers of SC-FDMA symbols accordingto CP lengths. For example, a slot can include 7 SC-FDMA symbols in thenormal CP case. The uplink subframe is divided into a control region anda data region in the frequency domain. The data region is allocated witha PUSCH and used to carry a data signal such as audio data. The controlregion is allocated a PUCCH and used to carry control information. ThePUCCH includes an RB pair located (e.g. m=0, 1, 2 and 3) at both ends ofthe data region in the frequency domain and hopped in a slot boundary.The control information includes HARQ ACK/NACK, CQI (channel qualityinformation), PMI (precoding matrix indicator), RO (rank indicator),etc.

FIG. 8 illustrates a carrier aggregation (CA) communication system.

Referring to FIG. 8, a plurality of uplink/downlink component carriers(CCs) can be aggregated to support a wider uplink/downlink bandwidth.The CCs may be contiguous or non-contiguous in the frequency domain.Bandwidths of the CCs can be independently determined. Asymmetrical CAin which the number of UL CCs is different from the number of DL CCs canbe implemented. Control information may be transmitted/received onlythrough a specific CC. This specific CC can be referred to as a primaryCC (PCC) and other CCs can be referred to as secondary CCs (SCCs). Forexample, when cross-carrier scheduling (or cross-CC scheduling) isapplied, a PDCCH for downlink allocation can be transmitted through DLCC#0 and a PDSCH corresponding to the PDCCH can be transmitted throughDL CC#2. The term “component carrier” can be replaced by otherequivalent terms (e.g. carrier, cell, etc.).

For cross-CC scheduling, a carrier indicator field (CIF) is used.Presence or absence of the CIF in a PDCCH can be determined by higherlayer signaling (e.g. RRC signaling) semi-statically and UE-specifically(or UE group-specifically). The baseline of PDCCH transmission issummarized as follows.

-   -   CIF disabled: a PDCCH on a DL CC is used to allocate a PDSCH        resource on the same DL CC or a PUSCH resource on a linked UL        CC.    -   No CIF    -   CIF enabled: a PDCCH on a DL CC can be used to allocate a PDSCH        or PUSCH resource on a specific DL/UL CC from among a plurality        of aggregated DL/UL CCs using the CIF.    -   LTE DCI format extended to have the CIF        -   CIF corresponds to a fixed x-bit field (e.g. x=3) (when the            CIF is set).        -   CIF position is fixed irrespective of DCI format size (when            the CIF is set).

When the CIF is present, the BS can allocate a PDCCH monitoring DL CC(set) to reduce BD complexity of the UE. For PDSCH/PUSCH scheduling, aUE can detect/decode a PDCCH only in the corresponding DL CC. The BS cantransmit the PDCCH only through the monitoring DL CC (set). Themonitoring DL CC set can be set UE-specifically, UE-group-specificallyor cell-specifically.

FIG. 9 illustrates a case in which 3 DL CCs are aggregated and DL CC Ais set to a monitoring DL CC. When the CIF is disabled, each DL CC cancarry a PDCCH that schedules a PDSCH of the DL CC without the CIFaccording to LTE PDCCH rules. When the CIF is enabled through higherlayer signaling, only DL CC A can carry not only a PDSCH thereof butalso PDSCHs of other DL CCs using the CIF. DL CC B and DL CC C which arenot set to monitoring DL CCs do not carry a PDCCH. Here, the term“monitoring DL CC” can be replaced by the terms such as “monitoringcarrier”, “monitoring cell”. “scheduling carrier”, “scheduling cell”,“serving carrier”, “serving cell”, etc.

FIG. 10 illustrates an example of allocating downlink physical channelsto a subframe.

Referring to FIG. 10, a PDCCH (legacy PDCCH) according to legacy LTE canbe allocated to a control region of the subframe. A PDCCH can beadditionally allocated to a data region (e.g. a resource region for aPDSCH) of the subframe. The PDCCH allocated to the data region isreferred to as an advanced PDCCH (A-PDCCH) or enhanced PDCCH (E-PDCCH)for convenience. FIG. 10 illustrates a case in which one E-PDCCH ispresent through two slots of the subframe. However, this is exemplaryand an E-PDCCH can be present per slot. For example, an E-PDCCH for a DLgrant can be transmitted in the first slot and an E-PDCCH for a UL grantcan be transmitted in the second slot.

A description will be given of a method for allocating and operatingresources for a downlink control channel using the data region (e.g. aPDSCH) of a subframe with reference to the attached drawings. While thefollowing description focuses on the relationship between a BS and a UEfor convenience, the present invention is equally/similarly applicableto operations between a BS and a relay or between a relay and a UE.Accordingly, BS-UE can be replaced by BS-relay or relay-UE in thefollowing description. A relay and a UE can be generalized as a receiverin terms of signal reception. When the relay operates as a receiver, anE-PDCCH can be replaced by a relay-PDCCH (R-PDCCH).

The E-PDCCH will now be described in more detail. The E-PDCCH carriesDCI. For details of DCI, refer to Table 1. For example, the E-PDCCH cancarry downlink scheduling information and uplink scheduling information.A signal processing procedure using an E-PDCCH/PDSCH and a signalprocessing procedure using an E-PDCCH/PUSCH are identical/similar tosteps S107 and S108 of FIG. 1. That is, a UE can receive an E-PDCCH andthen receive data/control information through a PDSCH corresponding tothe E-PDCCH. In addition, the UE can receive the E-PDCCH and thenreceive data/control information through a PUSCH corresponding to theE-PDCCH. E-PDCCH transmission processing (e.g. channel coding,interleaving, multiplexing, etc.) can be performed using processing(refer to FIGS. 5 and 6) defined in LTE and modified as necessary.

LTE adopts a method of reserving a PDCCH candidate region (referred toas a PDCCH search space hereinafter) in a control region andtransmitting a PDCCH for a specific UE in part of the PDCCH searchspace. Accordingly, the UE can obtain the PDCCH corresponding theretowithin the PDCCH search space through blind decoding. Similarly, anE-PDCCH can also be transmitted through some or all reserved resources.

FIG. 11 illustrates a procedure of allocating resources for E-PDCCHs andreceiving the E-PDCCHs.

Referring to FIG. 11, a BS transmits E-PDCCH resource allocation (RA)information to UEs (S1210). The E-PDCCH RA information may include RB(or VRB (virtual resource block) allocation information. The RBallocation information can be provided per RB or RBG. The E-PDCCH RAinformation can be transmitted through higher layer (e.g. RRC)signaling. Here, the E-PDCCH RA information is used to reserve E-PDCCHresources (regions). Then, the BS transmits an E-PDCCH to each UE(S1220). The E-PDCCH can be transmitted within some or all E-PDCCHresource (e.g. M RBs) reserved in step S1210. Accordingly, thecorresponding UE monitors a resource (region) (referred to as an E-PDCCHsearch space, simply, search space, hereinafter) in which the E-PDCCHcan be transmitted (S1230). The E-PDCCH search space can be provided asa part of an RB set allocated in step S1210. Here, monitoring includesblind decoding of a plurality of E-PDCCH candidates in the search space.

DCI (e.g. a DL grant and UL grant) mapped to the E-PDCCH resource (e.g.RBs) may not be cross-interleaved. In this case, only a single E-PDCCHis transmitted through one or more RBs. In addition, the DCI mapped tothe E-PDCCH resource may be intra-RB-interleaved. Furthermore, the DCImapped to the E-PDCCH resource may be inter-RB-interleaved. In thiscase, a plurality of E-PDCCHs can be simultaneously transmitted throughone or more RBs.

The present invention proposes a method for efficiently configuring asearch space for an E-PDCCH. In the case of E-PDCCH, DCI and an RS canbe precoded together in order to obtain precoding gain. The E-PDCCH canbe transmitted such that only an E-PDCCH corresponding to one UE ispresent in one RB (non-cross interleaving) in order to obtain frequencyselective scheduling gain (MU-MIMO in which plural E-PDCCH arediscriminated according to beamforming may be an exception). The R-PDCCHis transmitted in a PDSCH region and the E-PDCCH can be replaced by theR-PDCCH in the specification.

The E-PDCCH search space can be limited to a set of specific RBs becausean excessively large number of E-PDCCH blind decoding operations areneeded if the entire band is configured as the search space. The RB setfor the search space can be semi-statically determined and may bechanged on a subframe-by-subframe basis through a pseudo-random hoppingprocedure according to a UE-specific parameter.

A description will be given of a method for determining a candidateposition in which an E-PDCCH can be transmitted in an RB set determinedfor an E-PDCCH search space within one subframe. The candidate positioncan be given per aggregation level. Here, the candidate position canrefer to a resource through which an E-PDCCH (candidate) is transmittedor a resource index indicating the resource through which the E-PDCCH(candidate) is transmitted. The E-PDCCH (candidate) is transmitted usingone or more resource units (e.g. RBs, RB pairs, CCEs) according toaggregation level. When the E-PDCCH (candidate) is transmitted using aplurality of resource units, the candidate position can be specified bya resource set consisting of the plurality of resource units or aspecific resource unit representative of the plurality of resourceunits. Unless otherwise mentioned, the term candidate position is usedinterchangeably with the terms E-PDCCH and E-PDCCH candidate in thespecification.

It is assumed that an E-PDCCH corresponding to aggregation level L istransmitted through L RBs in the following description for convenience.In addition, it is assumed that when N RBs are indexed as #0, #1, . . ., #N−1 when the N RBs configure a search space. The RBs for the searchspace can be mapped to PRBs according to an appropriate mapping rule (inthis case, an RB means a VRB). A VRB-to-PRB mapping method may includelocalized VRB mapping and distributed VRB mapping of LTE.

A simple method of configuring the search space using the N RBs is tosequentially aggregate RBs starting from index #0 to configure candidatepositions at each aggregation level. That is, in the case of an E-PDCCHcorresponding to aggregation level 1, each of RBs #0, #1, . . . , #L₁−1can be set as one E-PDCCH candidate position. In the case of an E-PDCCHsearch space corresponding to aggregation level 2, [RB #0, RB #1], [RB#2, RB #3], [RB #2*L₂−2, RB #2*L₂−1] can be respectively set as E-PDCCHcandidate positions. Search spaces corresponding to aggregation levels 4and 8 can be configured through the same principle. Here, L_(k) denotesthe number of candidate positions at aggregation level k, k representingan aggregation level.

FIG. 12 illustrates configuration of search spaces when L₁=6, L₂=6, L₄=2and L₈=2. In FIG. 12, it is assumed that 15 RBs (e.g. VRBs) areallocated in step S1210 of FIGS. 11. 6, 12, 8 and 16 RBs are necessaryto transmit E-PDCCH candidates for respective aggregation levels sinceL₁=6, L₂=6, L₄=2 and L₈=2. Referring to FIG. 12, RBs (e.g. VRBs)necessary for E-PDCCH candidate transmission at each aggregation levelare consecutively allocated starting from index #0. In FIG. 12, a numberin a box represents an E-PDCCH candidate index or candidate positionindex. A UE sequentially blind-decodes E-PDCCH candidates at eachaggregation level in order to check an E-PDCCH allocated thereto.

The search space configuration method illustrated in FIG. 12 isinefficient in the case of localized virtual resource block (LVRB)mapping (i e n_(PRB)=n_(VRB)) by which RBs (i.e. VRBs) configuring asearch space are mapped to PRBs (physical resource blocks). Here,n_(PRB) denotes a PRB index and n_(VRB) denotes a VRB index.Specifically, at aggregation level 1, 6 candidate positions areconcentrated on lower RB indices. Consequently, RBs corresponding to RBindices #6 to #15 cannot be used for E-PDCCH transmission even thoughthe RBs are available, which is inefficient for frequency selectivescheduling. Particularly, when LVRB mapping is used, there is highprobability of similar channel states for RB indices close to eachother, and thus inefficiency of the above-described search spaceconfiguration scheme in terms of frequency selective schedulingincreases.

To solve this problem, the present invention proposes arrangement ofnon-consecutive candidate positions in at least part of a resource unitset (e.g. RB set) for a search space. Here, arrangement ofnon-consecutive candidate positions includes placement ofnon-consecutive E-PDCCH (candidates) per E-PDCCH or per resource unit(e.g. RB) constituting an E-PDCCH. For example, if an RB is designatedas a candidate position in a search space corresponding to a specificaggregation level, the next RB may not be designated as a candidateposition. In this case, one RB may not be designated as a candidateposition or RBs corresponding to the specific aggregation level may notbe designated as candidate positions. Accordingly, candidate positionsof the specific aggregation level can be uniformly distributed in the RBset. Particularly, the search space configuration method may beadvantageous for a search space corresponding to a low aggregationlevel.

FIG. 13 illustrates application of the above-described method toaggregation levels 1, 2 and 4 of FIG. 12. In the case of aggregationlevel 1, an RB that is not designated as a candidate position is presentbetween candidate positions #0 and #1 and between candidate positions #1and #2. In addition, an RB that is not designated as a candidateposition is present between candidate positions #3 and #4 and betweencandidate positions #4 and #5. Three RBs that are not defined ascandidate positions are present between candidate positions #2 and #3 inorder to configure the RB set in a symmetrical structure. Candidatepositions #3, #4 and #5 may be respectively defined as RBs #6, #8 and#10 as necessary. This principle can be applied to aggregation levels 2and 4 such that candidate positions can be spaced as far apart aspossible within the given RB set.

The scheme illustrated in FIG. 12 has a disadvantage that consecutiveRBs are used even at a high aggregation level. Considering thataggregation levels 4 and 8 are used for poor channel states in general,utilization of frequency diversity using distributed RBs may bepreferable to frequency selective scheduling using consecutive RBs.Accordingly, the present invention proposes a method of settingcandidate positions in such a manner that candidate positionsalternately use resource units (e.g. RBs) for an E-PDCCH. For example,at aggregation level L, M RBs can be alternately allocated to candidatepositions before L RBs are assigned to one position. Here, M is thedivisor of L. For example, if an aggregation level L is 8, then M may be1, 2 or 4. This scheme is applicable only to some aggregation levels.

FIG. 14 illustrates application of the above-described method toaggregation levels 2, 4 and 8 of FIG. 12. Through this method, RBscorresponding to one candidate position can be spaced as far apart aspossible to obtain frequency diversity gain.

It is possible to combine the schemes illustrated in FIGS. 13 and 14 toconfigure a search space. For example, the scheme of FIG. 13 can be usedat a specific aggregation level and the scheme of FIG. 14 can be used ata different aggregation level. An RB set used to determine candidatepositions at a specific aggregation level can be determined using thescheme of FIG. 13 and an RB used for each candidate position in the RBset can be determined using the scheme of FIG. 14.

FIG. 15 illustrates a hybrid of the schemes of FIGS. 13 and 14.Referring to FIG. 15, the scheme of FIG. 13 is applicable to aggregationlevels 1 and 2 and the scheme of FIG. 14 is applicable to aggregationlevel 8. In the case of aggregation level 4, an RB set (i.e. RBs #0, #1,#2, #3, #8, #9, #10 and #11) can be determined using the scheme of FIG.13 and RBs within the RB set can be alternately allocated to a pluralityof (e.g. 2) candidate positions, as illustrated in FIG. 14. In otherwords, at aggregation level 4, a plurality of (e.g. L₄(=2)) subsets eachof which consists of 4 RBs corresponding to the aggregation level arenon-consecutively configured, preferably, spaced as far apart aspossible and M (e.g. M=1) RB is alternately allocated to candidatepositions in each subset, as illustrated in FIG. 14.

FIG. 16 illustrates a modification of the scheme of FIG. 15.

Referring to FIG. 16, at aggregation level 4, RBs #4, #5, #12 and #13instead of RBs #2, #3, #10 and #11 are used such that RBs occupied bycandidate positions can be spaced as far apart as possible. In otherwords, N RBs can be divided into RB subsets each of which consists of L₄(=2) consecutive RBs and a number of (e.g. 4) RB subsets necessaryaccording to aggregation level can be selected such that the RB subsetsare spaced as far apart as possible. Each candidate position canalternately occupy the RBs in each subset, as illustrated in FIG. 14.Accordingly, frequency diversity gain of aggregation level can increase.

In the above-described search space determination method, it is assumedthat N RB sets are circular sets. That is, it can be assumed that RBs#0, #1, . . . are repeated after RB #N−1 and the spacing between RB #0and RB #N−1 corresponds to one index. This assumption is suitable to acase in which a search space is hopped on a subframe-by-subframe basisbecause an RB hopped to RB #N+k can be easily mapped to RB #k through amodulo N computation. Otherwise, it can be assumed that N RBs are linearsets and thus no RB is present after RB #N−1. In this case, the spacingbetween RB #0 and RB #N−1 can be assumed to be N−1 indices. Thisassumption is suitable for a case in which a search space issemi-statically fixed.

While it is assumed that the E-PDCCH corresponding to aggregation levelL is transmitted using L RBs in the above description, the presentinvention is not limited thereto. For example, one RB (or RB pair) canbe divided into a plurality of subsets and the E-PDCCH corresponding toaggregation level L can be transmitted using L subsets. Here, a subsetcorresponds to a basic resource unit for E-PDCCH transmission and can bereferred to as an advanced control channel element (A-CCE), enhanced CCE(E-CCE) or simply CCE. A description will be given of a case in which anRB subset (i.e. A-CCE or E-CCE) is used as a basic resource unit forE-PDCCH transmission.

The E-PDCCH of aggregation level L can be transmitted using L subsetswhile the subsets respectively belong to different RBs. This scheme iseffective to obtain frequency diversity since the E-PDCCH is transmittedusing a plurality of RBs. To achieve this, a preconfigured RB set can bedivided into subsets and an additional index can be assigned to eachsubset. Then, the above-described scheme can be equally applied if theRB indices in FIGS. 12 to 16 are replaced by subset indices.

FIG. 17 illustrates search space configuration when one RB consists oftwo subsets. FIG. 17 corresponds to the scheme of FIG. 16.

Referring to FIG. 17, in the case of aggregation level 1, candidatepositions correspond to different RBs. While frequency selective E-PDCCHplacement cannot be performed when a plurality of candidate positionscorrespond to one RB, the E-PDCCH is easily transmittedfrequency-selectively since only one candidate position corresponds toone RB according to this scheme. In the case of aggregation level 2,since two subsets of each candidate position are allocated to the sameRB, the same precoding scheme is applicable to the two subsets.Accordingly, effective beamforming for E-PDCCH transmission can beperformed if the BS knows channel information. In the case ofaggregation levels 4 and 8, E-PDCCHs are transmitted using subsetsbelonging to RBs which are spaced apart, and thus frequency diversity isobtained. The above-described operation is applicable to a case in whichone RB (or RB pair) is divided into three or more subsets.

As described above, non-consecutive placement of starting points ofcandidate positions with a gap may be effective at a single aggregationlevel. In one embodiment, the gap can be determined by the aggregationlevel or the number of subsets (e.g. A-CCEs or E-CCEs) included in oneRB (or RB pair). For example, if one RB (or RB pair) includes K subsets,gap (or offset) of a*K+K−1 (a=0, 1, 2, . . . ) can be applied betweenstarting points of candidate positions at the corresponding aggregationlevel. The start points of candidate positions can be appropriatelydistributed to correspond to different RBs by applying a gap thereto.Referring to FIG. 17, a=0 at aggregation levels 1 and 2 (i.e. gap is 1)when K=2. For candidate positions 2 and 3, a=1 is set and thus the gaptherebetween becomes 3. This serves to distribute candidate positionsover 8 RBs configured for a search space more uniformly. As illustratedin FIG. 17, different gaps can be set for respective aggregation levelsand a different value can be given as a gap at a specific position forcandidate position optimization.

When an excessively large number of RBs is configured as a search space,the number of RBs on which a UE performs channel estimation increasesand thus implementation of the UE may become very complicated.Accordingly, the BS can detect a maximum number of RBs on which the UEcan perform channel estimation in the search space and configure anumber of RB sets belonging to the search space, which is equals to orless than the maximum number. For example, when the number of candidatepositions of aggregation level k is L_(k), the maximum number of RBsbelonging to the search space can be given as max{k*L_(k)} for k=1, 2, 4and 8. Here, k*L_(k) denotes the number of RB sets which the searchspace of aggregation level k spans on the assumption that subsetsconstituting all candidate positions are present in different RBs ataggregation level k. That is, the channel estimation performance of UEis specified based on a maximum value of k*L_(k) (k=1, 2, 4 and 8). Forexample, when L₁=6, L₂=6, L₄=2 and L₈=2, k*L_(k) is set to 6, 12, 8 and16, respectively, and thus the maximum number of RBs belonging to thesearch space is limited to 16. If candidate positions of a highaggregation level such as aggregation level 8 are not present in anE-PDCCH search space or all subsets are not transmitted throughdifferent RBs even though the candidate positions are present (e.g.E-PDCCH corresponding to aggregation level 8 is transmitted using twosubsets in one RB), a specific aggregation level can be excluded in theprocedure of determining the maximum number of RBs belonging to thesearch space. For example, if aggregation level 8 is excluded in theabove example, the maximum number of RBs belonging to the search spacecan be 12. This restriction can be imposed per common search space orUE-specific search space. In addition, this restriction can be imposedper component carrier or CoMP cell in a carrier aggregation environmentor CoMP environment.

While it is assumed that subset indices are sequentially given accordingto RB index in FIG. 17, the present invention is not limited thereto andthere are various methods for indexing subsets. For example, the firstsubsets of respective RBs are indexed first and then the second subsetsare indexed.

In the above-described operation, RB and/or subset indices can bechanged on a subframe basis according to parameters such as a subframeindex, C-RNTI of the UE or cell ID. For example, an offset valueindependently given per subframe can be applied to RB indices or subsetindices when candidate positions of a specific UE are determined.

FIG. 18 illustrates an example of changing candidate positions using anoffset value.

Referring to FIG. 18, offset 1 is applied to aggregation level 1, offset0 is applied to aggregation levels 2 and 8 and offset 2 is applied toaggregation level 4 while the RB indices are maintained (i.e. offsetvalue is fixed to 0). Consequently, candidate positions of aggregationlevel 1 correspond to odd-numbered subsets in FIG. 18, distinguishedfrom FIG. 17. In this case, E-PDCCH blocking does not occur between a UEthat searches even-numbered subsets for the E-PDCCH of aggregation levelland a UE that searches odd-numbered subsets for the E-PDCCH ofaggregation level 1. E-PDCCH blocking refers to absence of an E-PDCCHresource that can be allocated for E-PDCCH transmission of a UE sinceresources in a search space are used for E-PDCCH transmission foranother UE. The operation with respect to aggregation level 1 isapplicable to aggregation level 4.

The offset value illustrated in FIG. 18 can be changed based on subframe(subframe-wise offset). Referring to FIGS. 17 and 18, FIG. 17 isapplicable to a specific subframe and FIG. 18 is applicable to anothersubframe. The offset value applied to the search space can be setdifferently for each aggregation level as illustrated in FIG. 18. Theoffset value can be determined according to a specific seed value. Forexample, when the seed value is set to s, the offset value ofaggregation level L can be given as s*L. Subframe-wise offset may not beused as necessary. For example, if multiple cells have different offsetvalues when the multiple cells simultaneously transmit E-PDCCHs, it maybe difficult to perform joint transmission. In this case, the BS canconfigure whether or not the subframe-wise offset is applied through ahigher layer such as RRC for more effective operation.

The above-described gap (or offset) between candidate positions can bevaried. For example, the presence or absence of the gap or the size ofthe gap can depend on a system bandwidth or the size of an RB set (i.e.the number of RBs) allocated for E-PDCCH transmission. For example, ifno gap (or offset) is present between candidate positions, as shown inFIG. 12, the E-PDCCH search space is generated using consecutive RBs orsubset indices, and thus the size of the RB set occupied by the E-PDCCHsearch space decreases. If the search space of aggregation level 1 isconfigured using positions corresponding to indices 0 to 5 and one RBincludes two subsets, the search space of aggregation level 1 can beconfigured using a total of three RBs. Here, a gap of size 1 is givenbetween candidate positions of aggregation level 1, a total of six RBscan be used since the search space of aggregation level 1 is configuredusing positions corresponding to indices {0, 2, 4, 6, 8, 10}.Accordingly, if the system bandwidth is narrow or the size of the RB setallocated for the E-PDCCH search space is small (e.g. if the size of RBset is set to lower than a predetermined reference value), the searchspace is advantageously configured with only a small number of RBswithout having a gap since the number of RBs that can be used for PDSCHtransmission can be secured, for example. On the other hand, if thesystem bandwidth is wide or the size of RB set allocated for the E-PDCCHsearch space is large (e.g. if the RB set size is set to greater thanthe predetermined reference value), candidate positions areadvantageously uniformly distributed over a large number of RBs with anappropriate gap for frequency selective E-PDCCH transmission. That is,as the system bandwidth or E-PDCCH search space RB set size increases, alarger gap can be set between candidate positions. Otherwise, in orderto flexibly set a gap that the BS desires, the gap between candidatepositions can be signaled through a higher layer signal such as an RRCsignal.

FIG. 19 illustrates an example of configuring a search space with anappropriate gap present between candidate positions. FIG. 19 assumesthat four CCEs are configured from one PRB pair. Referring to FIG. 19,CCEs necessary for E-PDCCH candidate transmission at each aggregationlevel are consecutively allocated starting from index #0. Here, a gap isapplied between E-PDCCH candidate positions and thus the E-PDCCHcandidate positions are non-consecutively distributed in the CCE domain.

The method of providing a gap between candidate positions, proposed bythe present invention, is applicable to a method of transmittingE-PDCCHs in a distributed manner.

FIG. 20 illustrates an example of applying a gap between candidatepositions to transmit E-PDCCHs in a distributed manner. Referring toFIG. 20, in the case of aggregation level 2, one CCE is extracted fromeach of two different PRB pairs to configure a candidate position, andthus DCI can be transmitted using resources spaced apart in thefrequency domain. In this case, a predetermined gap (e.g. 1 CCE in thecase of aggregation level 2) can be provided between candidate positionssuch that candidate positions are uniformly distributed through allE-PDCCH PRB pairs. If only one CCE for a candidate position aggregationlevel 2 can be allocated to one PRB pair since a sufficient number ofPRB pairs is set, which is not shown, candidate positions can bedistributed in a wider frequency region. For example, candidate position#0 can be configured with CCE #0 and CCE #4 and candidate position #1can be configured with CCE #8 and CCE #12. This principle isequally/similarly applicable to aggregation levels 4 and 8.

The method of applying a gap between candidate positions, proposed bythe present invention, is applicable to a case in which CCE indexing isperformed in a different manner.

FIG. 21 illustrates non-sequential CCE indexing in search spaceconfiguration. FIG. 21 assumes a case in which three PRB pairs areprovided through RRC for E-PDCCH transmission and four CCEs areconfigured from each PRB pair. Referring to FIG. 21, the PRB pairs areindexed in such a manner that second CCEs of the PRB pairs are indexedupon indexing of first CCEs of the PRB pairs. In this case, candidatepositions #0, #1 and #2 are configured using consecutive CCEs (i.e. withzero gap) and candidate position #3 is configured with a gap (i.e.offset) corresponding to three CCEs from candidate position #2 ataggregation level 1. This prevents CCEs used for candidate positions ofaggregation level 1 from overlapping with CCEs used for candidatepositions of aggregation level 2 so as to reduce E-PDCCH blockingprobability. For example, if a gap is not applied at aggregation level1, CCE #3 is assigned as a resource for candidate position #3. In thiscase, candidate positions #0 and #3 of aggregation level 1, whichcorrespond to candidate position #0 of aggregation level 2, cannot beused for actual transmission if candidate position #0 of aggregationlevel 2 is used for actual transmission. However, when a gap is appliedto aggregation level 1, as described above, candidate positions #0 and#3 of aggregation level 1 can be used even if candidate position #0 ofaggregation level 2 is used for actual transmission. When CCE indexingis performed as illustrated in FIG. 21, if N PRB pairs are set forlocalized E-PDCCH transmission of aggregation level L, CCEs #n, #n+N,#n+2N, #n+(L−1)N can be used.

An operation similar to FIG. 21 can be implemented without a gap betweencandidate positions, which is illustrated in FIG. 22. In the example ofFIG. 22, candidate positions can be configured using consecutive CCEswithout a gap between candidate positions. Referring to FIG. 22, sixcandidate positions are configured using CCEs #0 to #5 at aggregationlevel 1. In this case, two CCEs can be aggregated with a predeterminedspacing in each PRB pair in order to avoid a case in which CCEs used foraggregation level 2 correspond to candidate positions of aggregationlevel 1. That is, CCE #n and CCE #n+2L can be aggregated to configurecandidates of aggregation level 2. Whether the operation of aggregatingCCEs with a spacing in the same PRB pair is applied or not can depend onthe number of CCEs configured in one PRB pair or aggregation level.

When two CCEs are configured from one PRB pair, as illustrated in FIG.23, CCEs can be combined without a gap since the correspondingaggregation level can be possible when all CCEs belonging to one PRBpair are used. When two CCEs are configured from one PRB pair, asillustrated in FIG. 23, two PRB pairs are needed to configure acandidate of aggregation level 4. In this case, a PRB pair to which aCCE spaced apart by a predetermined distance from a CCE corresponding tothe starting point of aggregation can be used. For example, when N (e.g.N=5) PRB pairs are set as an E-PDCCH transmission region, if it isassumed that four CCEs starting from CCE #n (e.g. CCE #0) areaggregated, CCE #n+N (e.g. CCE #6) belonging to the same PRB pair isused first and then CCE #n+N/2 (e.g. CCE #3) and CCE #n+N/2+N (e.g. CCE#9), obtained by adding an offset (N/2=3 in FIG. 23) corresponding tohalf the number of all PRB pairs to the CCE index, are used to configurecandidate positions. A floor function may be applied to make the CCEindices integers as necessary. This scheme is applicable when two ormore PRB pairs need to be used since a corresponding candidate positionscannot be configured even when all CCEs belonging to one PRB pair areused (when candidate positions of aggregation level 8 are configured inthe case of generation of four CCEs per PRB pair). In this case, if onecandidate position is configured using K PRB pairs, the offset value canbe N/K or an integer close thereto. In other words, CCEs spaced apart bythe offset (or resources in corresponding PRB pairs) can be used tocomplement insufficient CCEs. Here, the offset value is set to N/Kbecause collision with a CCE used for a different candidate position canbe reduced by additionally using a CCE which is considerably spacedapart from among all CCEs since CCEs of consecutive indices areaggregated to configure one candidate position.

FIGS. 24 and 25 illustrate search space configuration according to theprinciple of the present invention when CCE indices are preferentiallyassigned to PRB pairs. Here, a localized candidate refers to a case inwhich one candidate belongs to one PRB pair and a distributed candidaterefers to a case in which one candidate belongs to a plurality of PRBpairs. A predetermined offset can be applied between starting CCEindices of search spaces of aggregation levels to avoid overlap of CCEsbetween search spaces of different aggregation levels, which is notshown.

FIG. 24 shows a localized candidate case. Here, k-th E-PDCCH candidateof aggregation level L uses CCEs #n_(k,L), #n_(k,L)+N, . . . ,#n_(k,L)+(L−1)N and neighboring starting points can have a relationshipof CCE n_(k+,L)=CCE n_(k,L)+T (e.g. T=1) without a gap therebetween.

Expression 1 represents a CCE configuring k-th candidate of aggregationlevel L.

(Y+k+i*N)mod A  [Expression 1]

Here, Y denotes an offset value for the corresponding search space andcan be independently given per aggregation level, k represents the k-thE-PDCCH candidate, i is 0, 1, . . . , L−1 and N represents the number ofRBs (RB pairs) configured for E-PDCCH transmission. Here, an RB (RBpair) includes a VRB (VRB pair) or a PRB (PRB pair). In addition, Adenotes the number of CCEs configured for E-PDCCH transmission.

While Expression 1 represents a case in which no gap is present betweenstarting points of neighboring E-PDCCHs, this is exemplary and apredetermined gap (=T=1) can be given between neighboring E-PDCCHs.

Expression 2 represents a CCE configuring the k-th candidate ofaggregation level L when a gap (T) is present between starting points ofneighboring E-PDCCHs.

(Y+Tk+i*N)mod A  [Expression 2]

Here, Y, k, i, N and A are defined in the same manner as inExpression 1. T is a positive integer and can be set to a value lessthan L. Here, T representing the gap can be a parameter varyingaccording to aggregation level, the number of CCEs per PRB pair, thenumber of PRB pairs configured as an E-PDCCH search space, etc.

FIG. 25 illustrates a distributed candidate case. Here, the k-thcandidate of aggregation level L uses CCEs #n_(k,L), #n_(k,L)+1, . . . ,#n_(k,L)+(L−1) and a gap corresponding to the corresponding aggregationlevel is present between starting points of E-PDCCH candidates. Forexample, the starting points of E-PDCCH candidates can have arelationship of CCE #n_(k+1,L)=CCE #n_(k,L)+L+T−1. Here, T is anadditional gap applied between the starting points of E-PDCCHcandidates. When an additional gap is not present, T can be set to 1.

Expression 3 represents a CCE configuring the k-th candidate ofaggregation level L.

(Y+L*k+i)mod A  [Expression 3]

Here, Y represents an offset value for the corresponding search spaceand can be independently given per aggregation level. L denotes theaggregation level, k represents the k-th E-PDCCH candidate ofaggregation level L, i is 0, 1, . . . , L−1, and A denotes the number ofCCEs configured for E-PDCCH transmission.

Expression 4 represents a CCE configuring the k-th candidate ofaggregation level L when the gap T is present between starting points ofE-PDCCHs.

(Y+T*k+i)mod A  [Expression 4]

Here, Y, L, k, i and A are defined in the same manner as in Equation 3.T is a positive integer and can be set to a value less than L. Here, Trepresenting the gap can be a parameter varying according to aggregationlevel, the number of CCEs per PRB pair, the number of PRB pairsconfigured as an E-PDCCH search space, etc.

While it is assumed that a CCE corresponding to a basic aggregation unitis derived from one PRB pair when distributed candidates are configuredin the above-described example, the search space configuration scheme isapplicable to other cases. That is, the search space configurationscheme can be applied to a case in which individual CCEs configuringdistributed candidates are composed of REs of a plurality of PRB pairs.

For example, CCEs are indexed and then a search space can be configuredaccording to the above-described operation principle based on the CCEindex (that is, appropriate CCE indices are collected according towhether candidates are localized candidates or distributed candidatesand an appropriate gap is applied between starting points of E-PDCCHcandidates). In this case, K CCEs for localized candidates, which arepositioned in different PRB pairs, can be redistributed to configure KCCEs for distributed candidates in order to index CCEs in the samemanner as CCEs for localized candidates, which are composed of REs in asingle PRB pair.

FIG. 26 illustrates configuration of a CCE by combining RE sets in a PRBpair.

Referring to FIG. 26, each PRB pair is divided into a predeterminednumber of RE sets and RE sets are combined to configure a CCE. Forexample, RE sets A and E in PRB pair #m are combined to configurelocalized type CCE #a and the same operation is repeated on PRB pair #nto configure localized type CCE #b. For distributed type CCEconfiguration, RE set A of PRB pair #m and RE set E of PRB pair #n arecombined to configure distributed type CCE #a and RE set A of PRB pair#n and RE set E of PRB pair #m are combined to configure distributedtype CCE #b. K (e.g. K=2) distributed CCEs configured in this mannerrespectively occupy indices of K localized CCEs (i.e. K localized CCEswhich can be configured through the same RE set) corresponding thereto.Accordingly, even when distributed candidate CCEs are transmittedthrough a plurality of PRB pairs, the distributed candidate CCEs can beindexed while coexisting with localized candidate CCEs and can configurea search space according to the above-described proposed scheme.

FIG. 27 illustrates a BS, a relay and a UE applicable to the presentinvention.

Referring to FIG. 27, a wireless communication system includes a BS 110and a UE 120. When the wireless communication system includes a relay,the BS or UE can be replaced by the relay.

The BS 110 includes a processor 112, a memory 114 and a radio frequency(RF) unit 116. The processor 112 may be configured to implement theprocedures and/or methods proposed by the present invention. The memory114 is connected to the processor 112 and stores information related tooperations of the processor 112. The RF unit 116 is connected to theprocessor 112 and transmits and/or receives an RF signal. The UE 120includes a processor 122, a memory 124 and an RF unit 126. The processor112 may be configured to implement the procedures and/or methodsproposed by the present invention. The memory 124 is connected to theprocessor 122 and stores information related to operations of theprocessor 122. The RF unit 126 is connected to the processor 122 andtransmits and/or receives an RF signal.

The embodiments of the present invention described hereinbelow arecombinations of elements and features of the present invention. Theelements or features may be considered selective unless otherwisementioned. Each element or feature may be practiced without beingcombined with other elements or features. Further, an embodiment of thepresent invention may be constructed by combining parts of the elementsand/or features. Operation orders described in embodiments of thepresent invention may be rearranged. Some constructions of any oneembodiment may be included in another embodiment and may be replacedwith corresponding constructions of another embodiment. It will beobvious to those skilled in the art that claims that are not explicitlycited in each other in the appended claims may be presented incombination as an embodiment of the present invention or included as anew claim by a subsequent amendment after the application is filed.

In the embodiments of the present invention, a description is madecentering on a data transmission and reception relationship among a BS,a relay, and an MS. In some cases, a specific operation described asperformed by the BS may be performed by an upper node of the BS. Namely,it is apparent that, in a network comprised of a plurality of networknodes including a BS, various operations performed for communicationwith an MS may be performed by the BS, or network nodes other than theBS. The term ‘BS’ may be replaced with the term ‘fixed station’, ‘NodeB’, ‘enhanced Node B (eNode B or eNB)’, ‘access point’, etc. The term‘UE’ may be replaced with the term ‘Mobile Station (MS)’, ‘MobileSubscriber Station (MSS)’, ‘mobile terminal’, etc.

The embodiments of the present invention may be achieved by variousmeans, for example, hardware, firmware, software, or a combinationthereof. In a hardware configuration, the methods according to theembodiments of the present invention may be achieved by one or moreApplication Specific Integrated Circuits (ASICs), Digital SignalProcessors (DSPs), Digital Signal Processing Devices (DSPDs),Programmable Logic Devices (PLDs), Field Programmable Gate Arrays(FPGAs), processors, controllers, microcontrollers, microprocessors,etc.

In a firmware or software configuration, the embodiments of the presentinvention may be implemented in the form of a module, a procedure, afunction, etc. For example, software code may be stored in a memory unitand executed by a processor. The memory unit is located at the interioror exterior of the processor and may transmit and receive data to andfrom the processor via various known means.

Those skilled in the art will appreciate that the present invention maybe carried out in other specific ways than those set forth hereinwithout departing from the spirit and essential characteristics of thepresent invention. The above embodiments are therefore to be construedin all aspects as illustrative and not restrictive. The scope of theinvention should be determined by the appended claims and their legalequivalents, not by the above description, and all changes coming withinthe meaning and equivalency range of the appended claims are intended tobe embraced therein.

INDUSTRIAL APPLICABILITY

The present invention is applicable to a UE, a BS or other apparatusesof a wireless communication system. Specifically, the present inventioncan be applied to a method for transmitting uplink control informationand an apparatus for the same.

1-14. (canceled)
 15. A method for receiving a downlink control channelby a communication device in a wireless communication system, the methodcomprising: determining a resource set for control information, theresource set for control information including a control channel elementset; and monitoring downlink control channel candidates on the controlchannel element set of the resource set for control information in atime unit to detect the downlink control channel, wherein the downlinkcontrol channel candidates include n^(th) and (n+1)^(th) downlinkcontrol channel candidates of an aggregation level, wherein a spacingbetween starting positions of the n^(th) and (n+1)^(th) downlink controlchannel candidates of the aggregation level on the control channelelement set depends on a number of control channel elements in theresource set for control information.
 16. The method of claim 15,wherein the resource set for control information is defined by aresource block set and an orthogonal frequency division multiplexing(OFDM) symbol set in one time unit
 17. The method of claim 15, whereinat least part of resources other than the resource set for controlinformation in a bandwidth of the time unit are used for physicaldownlink shared channel (PDSCH) transmission.
 18. The method of claim15, wherein the n^(th) and (n+1)^(th) downlink control channelcandidates of the aggregation level are discontinuous on the controlchannel element set.
 19. The method of claim 15, wherein each of then^(th) and (n+1)^(th) downlink control channel candidates of theaggregation level consists of L consecutive control channel elements,and L represents the aggregation level.
 20. The method of claim 15,wherein the downlink control channel candidates include physicaldownlink control channel candidates, and the downlink control channelincludes an PDCCH.
 21. A communication apparatus for use in a wirelesscommunication system, comprising: a radio frequency (RF) unit; and aprocessor configured to: determine a resource set for controlinformation, the resource set for control information including acontrol channel element set, and monitor downlink control channelcandidates on the control channel element set of the resource set forcontrol information in a time unit to detect the downlink controlchannel, wherein the downlink control channel candidates include n^(th)and (n+1)^(th) downlink control channel candidates of an aggregationlevel, wherein a spacing between starting positions of the n^(th) and(n+1)^(th) downlink control channel candidates of the aggregation levelon the control channel element set depends on a number of controlchannel elements in the resource set for control information.
 22. Thecommunication apparatus of claim 21, wherein the resource set forcontrol information is defined by a resource block set and an orthogonalfrequency division multiplexing (OFDM) symbol set in one time unit 23.The communication apparatus of claim 21, wherein at least part ofresources other than the resource set for control information in abandwidth of the time unit are used for physical downlink shared channel(PDSCH) transmission.
 24. The communication apparatus of claim 21,wherein the n^(th) and (n+1)^(th) downlink control channel candidates ofthe aggregation level are discontinuous on the control channel elementset.
 25. The communication apparatus of claim 21, wherein each of then^(th) and (n+1)^(th) downlink control channel candidates of theaggregation level consists of L consecutive control channel elements,and L represents the aggregation level.
 26. The communication apparatusof claim 21, wherein the downlink control channel candidates includephysical downlink control channel candidates, and the downlink controlchannel includes an PDCCH.